Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
Tributary is regular. It follows the -ies Conversion rule.
Use plural verbs: "The tributaries are ready" (not "is ready").
Yes. The plural tributaries is standard across all English variants.
The word tributary follows the standard English pluralization rule. When forming the plural, tributary becomes tributaries. This follows the -ies Conversion pattern, which is one of the most common plural rules in English.
Understanding why tributary becomes tributaries helps with spelling and pronunciation. Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
When using tributaries in writing, remember that it functions as a plural noun in sentences. It pairs with plural verbs and pronouns. For example: "The tributaries are ready" (not "is ready"). This subject-verb agreement is essential for grammatical correctness.